From 6ac82f8c1bd9070c8537a950205ed3741c539b7e Mon Sep 17 00:00:00 2001
From: Valentin Iovene <valentin@too.gy>
Date: Sun, 29 Mar 2020 15:50:19 +0200
Subject: [PATCH 01/16] BUG: fix GH33113, conversion of empty DataFrame to
 SparseDtype

---
 pandas/tests/extension/base/dtype.py | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/pandas/tests/extension/base/dtype.py b/pandas/tests/extension/base/dtype.py
index 154fcdc38826d..f196c9e80910c 100644
--- a/pandas/tests/extension/base/dtype.py
+++ b/pandas/tests/extension/base/dtype.py
@@ -123,3 +123,7 @@ def test_get_common_dtype(self, dtype):
         # still testing as good practice to have this working (and it is the
         # only case we can test in general)
         assert dtype._get_common_dtype([dtype]) == dtype
+
+    def test_astype_empty_dataframe(self, dtype):
+        empty_dataframe = pd.DataFrame()
+        assert empty_dataframe.astype(dtype) == empty_dataframe

From e76f1fc1ad060c66ee5f75ad28936d3f9d26ea5e Mon Sep 17 00:00:00 2001
From: Valentin Iovene <valentin@too.gy>
Date: Tue, 31 Mar 2020 00:51:05 +0200
Subject: [PATCH 02/16] return empty dataframe when nothing to concatenate

---
 pandas/core/generic.py               |  3 +++
 pandas/tests/extension/base/dtype.py | 20 ++++++++++++++++----
 2 files changed, 19 insertions(+), 4 deletions(-)

diff --git a/pandas/core/generic.py b/pandas/core/generic.py
index 1404d225eea97..c2bbfa07913ef 100644
--- a/pandas/core/generic.py
+++ b/pandas/core/generic.py
@@ -5548,6 +5548,9 @@ def astype(
             new_data = self._mgr.astype(dtype=dtype, copy=copy, errors=errors,)
             return self._constructor(new_data).__finalize__(self, method="astype")
 
+        if not results:
+            return pd.DataFrame()
+
         # GH 19920: retain column metadata after concat
         result = pd.concat(results, axis=1, copy=False)
         result.columns = self.columns
diff --git a/pandas/tests/extension/base/dtype.py b/pandas/tests/extension/base/dtype.py
index f196c9e80910c..f680c6282a65d 100644
--- a/pandas/tests/extension/base/dtype.py
+++ b/pandas/tests/extension/base/dtype.py
@@ -4,6 +4,7 @@
 import pytest
 
 import pandas as pd
+import pandas._testing as tm
 
 from .base import BaseExtensionTests
 
@@ -68,8 +69,17 @@ def test_check_dtype(self, data):
             {"A": pd.Series(data, dtype=dtype), "B": data, "C": "foo", "D": 1}
         )
 
-        # TODO(numpy-1.20): This warnings filter and if block can be removed
-        # once we require numpy>=1.20
+        # np.dtype('int64') == 'Int64' == 'int64'
+        # so can't distinguish
+        if dtype.name == "Int64":
+            expected = pd.Series([True, True, False, True], index=list("ABCD"))
+        else:
+            expected = pd.Series(
+                [True, True, False, False], index=list("ABCD")
+            )
+
+        # XXX: This should probably be *fixed* not ignored.
+        # See libops.scalar_compare
         with warnings.catch_warnings():
             warnings.simplefilter("ignore", DeprecationWarning)
             result = df.dtypes == str(dtype)
@@ -106,7 +116,9 @@ def test_construct_from_string(self, dtype):
         assert isinstance(dtype_instance, type(dtype))
 
     def test_construct_from_string_another_type_raises(self, dtype):
-        msg = f"Cannot construct a '{type(dtype).__name__}' from 'another_type'"
+        msg = (
+            f"Cannot construct a '{type(dtype).__name__}' from 'another_type'"
+        )
         with pytest.raises(TypeError, match=msg):
             type(dtype).construct_from_string("another_type")
 
@@ -126,4 +138,4 @@ def test_get_common_dtype(self, dtype):
 
     def test_astype_empty_dataframe(self, dtype):
         empty_dataframe = pd.DataFrame()
-        assert empty_dataframe.astype(dtype) == empty_dataframe
+        tm.assert_frame_equal(empty_dataframe.astype(dtype), empty_dataframe)

From 8a96a476f2b8523839c01e646d6511daf0e27a02 Mon Sep 17 00:00:00 2001
From: Valentin Iovene <valentin@too.gy>
Date: Tue, 31 Mar 2020 00:53:45 +0200
Subject: [PATCH 03/16] revert black formatting

---
 pandas/tests/extension/base/dtype.py | 8 ++------
 1 file changed, 2 insertions(+), 6 deletions(-)

diff --git a/pandas/tests/extension/base/dtype.py b/pandas/tests/extension/base/dtype.py
index f680c6282a65d..644c5491a8f17 100644
--- a/pandas/tests/extension/base/dtype.py
+++ b/pandas/tests/extension/base/dtype.py
@@ -74,9 +74,7 @@ def test_check_dtype(self, data):
         if dtype.name == "Int64":
             expected = pd.Series([True, True, False, True], index=list("ABCD"))
         else:
-            expected = pd.Series(
-                [True, True, False, False], index=list("ABCD")
-            )
+            expected = pd.Series([True, True, False, False], index=list("ABCD"))
 
         # XXX: This should probably be *fixed* not ignored.
         # See libops.scalar_compare
@@ -116,9 +114,7 @@ def test_construct_from_string(self, dtype):
         assert isinstance(dtype_instance, type(dtype))
 
     def test_construct_from_string_another_type_raises(self, dtype):
-        msg = (
-            f"Cannot construct a '{type(dtype).__name__}' from 'another_type'"
-        )
+        msg = f"Cannot construct a '{type(dtype).__name__}' from 'another_type'"
         with pytest.raises(TypeError, match=msg):
             type(dtype).construct_from_string("another_type")
 

From a4aad1444cea0190af0a5b2589e7c3409be1e44c Mon Sep 17 00:00:00 2001
From: Valentin Iovene <valentin@too.gy>
Date: Sun, 21 Jun 2020 15:49:49 +0200
Subject: [PATCH 04/16] restore-to-master

---
 pandas/tests/extension/base/dtype.py | 16 ++--------------
 1 file changed, 2 insertions(+), 14 deletions(-)

diff --git a/pandas/tests/extension/base/dtype.py b/pandas/tests/extension/base/dtype.py
index 644c5491a8f17..154fcdc38826d 100644
--- a/pandas/tests/extension/base/dtype.py
+++ b/pandas/tests/extension/base/dtype.py
@@ -4,7 +4,6 @@
 import pytest
 
 import pandas as pd
-import pandas._testing as tm
 
 from .base import BaseExtensionTests
 
@@ -69,15 +68,8 @@ def test_check_dtype(self, data):
             {"A": pd.Series(data, dtype=dtype), "B": data, "C": "foo", "D": 1}
         )
 
-        # np.dtype('int64') == 'Int64' == 'int64'
-        # so can't distinguish
-        if dtype.name == "Int64":
-            expected = pd.Series([True, True, False, True], index=list("ABCD"))
-        else:
-            expected = pd.Series([True, True, False, False], index=list("ABCD"))
-
-        # XXX: This should probably be *fixed* not ignored.
-        # See libops.scalar_compare
+        # TODO(numpy-1.20): This warnings filter and if block can be removed
+        # once we require numpy>=1.20
         with warnings.catch_warnings():
             warnings.simplefilter("ignore", DeprecationWarning)
             result = df.dtypes == str(dtype)
@@ -131,7 +123,3 @@ def test_get_common_dtype(self, dtype):
         # still testing as good practice to have this working (and it is the
         # only case we can test in general)
         assert dtype._get_common_dtype([dtype]) == dtype
-
-    def test_astype_empty_dataframe(self, dtype):
-        empty_dataframe = pd.DataFrame()
-        tm.assert_frame_equal(empty_dataframe.astype(dtype), empty_dataframe)

From d42709b3e1c0a3e699102fc1942fb721f045ceae Mon Sep 17 00:00:00 2001
From: Valentin Iovene <valentin@too.gy>
Date: Sun, 21 Jun 2020 15:55:06 +0200
Subject: [PATCH 05/16] return instance of class to handle frame or series

---
 pandas/core/generic.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/pandas/core/generic.py b/pandas/core/generic.py
index c2bbfa07913ef..bdda655193838 100644
--- a/pandas/core/generic.py
+++ b/pandas/core/generic.py
@@ -5549,7 +5549,7 @@ def astype(
             return self._constructor(new_data).__finalize__(self, method="astype")
 
         if not results:
-            return pd.DataFrame()
+            return self.__class__()
 
         # GH 19920: retain column metadata after concat
         result = pd.concat(results, axis=1, copy=False)

From 708fdc71951991e4c26bfdf13e971f9cd481bd6b Mon Sep 17 00:00:00 2001
From: Valentin Iovene <valentin@too.gy>
Date: Sun, 21 Jun 2020 15:59:49 +0200
Subject: [PATCH 06/16] add test

---
 pandas/tests/extension/test_sparse.py | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/pandas/tests/extension/test_sparse.py b/pandas/tests/extension/test_sparse.py
index f318934ef5e52..f62e7defa46c9 100644
--- a/pandas/tests/extension/test_sparse.py
+++ b/pandas/tests/extension/test_sparse.py
@@ -358,6 +358,10 @@ def test_astype_str(self, data):
     def test_astype_string(self, data):
         super().test_astype_string(data)
 
+    def test_astype_empty_frame(self, dtype):
+        empty_df = pd.DataFrame()
+        tm.assert_frame_equal(empty_df.astype(dtype), empty_df)
+
 
 class TestArithmeticOps(BaseSparseTests, base.BaseArithmeticOpsTests):
     series_scalar_exc = None

From 5b1fe9f3f8809b99b0a379ad67d643ad6d0280ab Mon Sep 17 00:00:00 2001
From: Valentin Iovene <valentin@too.gy>
Date: Sun, 21 Jun 2020 16:18:31 +0200
Subject: [PATCH 07/16] use type(self) instead of self.__class__

---
 pandas/core/generic.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/pandas/core/generic.py b/pandas/core/generic.py
index bdda655193838..17d25cb2ad9ce 100644
--- a/pandas/core/generic.py
+++ b/pandas/core/generic.py
@@ -5549,7 +5549,7 @@ def astype(
             return self._constructor(new_data).__finalize__(self, method="astype")
 
         if not results:
-            return self.__class__()
+            return type(self)()
 
         # GH 19920: retain column metadata after concat
         result = pd.concat(results, axis=1, copy=False)

From 738739e7274fc4f6d56c62ad229d7cea8d341db8 Mon Sep 17 00:00:00 2001
From: Valentin Iovene <valentin@too.gy>
Date: Sun, 21 Jun 2020 16:19:38 +0200
Subject: [PATCH 08/16] return self.copy()

---
 pandas/core/generic.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/pandas/core/generic.py b/pandas/core/generic.py
index 17d25cb2ad9ce..bf48410cd4815 100644
--- a/pandas/core/generic.py
+++ b/pandas/core/generic.py
@@ -5549,7 +5549,7 @@ def astype(
             return self._constructor(new_data).__finalize__(self, method="astype")
 
         if not results:
-            return type(self)()
+            return self.copy()
 
         # GH 19920: retain column metadata after concat
         result = pd.concat(results, axis=1, copy=False)

From a9e7e15c9503b4e7bca35adf4cb2b890df245493 Mon Sep 17 00:00:00 2001
From: Simon Hawkins <simonjayhawkins@gmail.com>
Date: Sun, 21 Jun 2020 19:47:15 +0100
Subject: [PATCH 09/16] move test to extension array tests

---
 pandas/tests/extension/base/casting.py | 6 ++++++
 pandas/tests/extension/test_sparse.py  | 4 ----
 2 files changed, 6 insertions(+), 4 deletions(-)

diff --git a/pandas/tests/extension/base/casting.py b/pandas/tests/extension/base/casting.py
index 567a62a8b33a5..d019df6146eb9 100644
--- a/pandas/tests/extension/base/casting.py
+++ b/pandas/tests/extension/base/casting.py
@@ -50,3 +50,9 @@ def test_to_numpy(self, data):
 
         result = pd.Series(data).to_numpy()
         self.assert_equal(result, expected)
+
+    def test_astype_empty_dataframe(self, dtype):
+        # https://github.com/pandas-dev/pandas/issues/33113
+        df = pd.DataFrame()
+        result = df.astype(dtype)
+        self.assert_frame_equal(result, df)
\ No newline at end of file
diff --git a/pandas/tests/extension/test_sparse.py b/pandas/tests/extension/test_sparse.py
index f62e7defa46c9..f318934ef5e52 100644
--- a/pandas/tests/extension/test_sparse.py
+++ b/pandas/tests/extension/test_sparse.py
@@ -358,10 +358,6 @@ def test_astype_str(self, data):
     def test_astype_string(self, data):
         super().test_astype_string(data)
 
-    def test_astype_empty_frame(self, dtype):
-        empty_df = pd.DataFrame()
-        tm.assert_frame_equal(empty_df.astype(dtype), empty_df)
-
 
 class TestArithmeticOps(BaseSparseTests, base.BaseArithmeticOpsTests):
     series_scalar_exc = None

From 9c7f06b38b7b6f66616eb0ee89238349b2c3be19 Mon Sep 17 00:00:00 2001
From: Simon Hawkins <simonjayhawkins@gmail.com>
Date: Sun, 21 Jun 2020 19:48:30 +0100
Subject: [PATCH 10/16] black fixup

---
 pandas/tests/extension/base/casting.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/pandas/tests/extension/base/casting.py b/pandas/tests/extension/base/casting.py
index d019df6146eb9..3aaf040a4279b 100644
--- a/pandas/tests/extension/base/casting.py
+++ b/pandas/tests/extension/base/casting.py
@@ -55,4 +55,4 @@ def test_astype_empty_dataframe(self, dtype):
         # https://github.com/pandas-dev/pandas/issues/33113
         df = pd.DataFrame()
         result = df.astype(dtype)
-        self.assert_frame_equal(result, df)
\ No newline at end of file
+        self.assert_frame_equal(result, df)

From 49280cbd8d11850b154c734713cc914aef8d944c Mon Sep 17 00:00:00 2001
From: Valentin Iovene <valentin@too.gy>
Date: Sun, 21 Jun 2020 20:57:25 +0200
Subject: [PATCH 11/16] add whatsnew entry

---
 doc/source/whatsnew/v1.1.0.rst | 1 +
 1 file changed, 1 insertion(+)

diff --git a/doc/source/whatsnew/v1.1.0.rst b/doc/source/whatsnew/v1.1.0.rst
index 567b6853bd633..17bb380a418e4 100644
--- a/doc/source/whatsnew/v1.1.0.rst
+++ b/doc/source/whatsnew/v1.1.0.rst
@@ -1068,6 +1068,7 @@ Sparse
 - Bug in :meth:`Series.sum` with ``SparseArray`` raises ``TypeError`` (:issue:`25777`)
 - Bug where :class:`DataFrame` containing :class:`SparseArray` filled with ``NaN`` when indexed by a list-like (:issue:`27781`, :issue:`29563`)
 - The repr of :class:`SparseDtype` now includes the repr of its ``fill_value`` attribute. Previously it used ``fill_value``'s  string representation (:issue:`34352`)
+- Fixed bug where :class:`DataFrame` or :class:`Series` could not be cast to :class:`SparseDtype` when empty (:issue:`33113`)
 
 ExtensionArray
 ^^^^^^^^^^^^^^

From f0f099c95b6b077153557a9cb50194981c521a5e Mon Sep 17 00:00:00 2001
From: Valentin Iovene <valentin@too.gy>
Date: Sun, 21 Jun 2020 22:02:09 +0200
Subject: [PATCH 12/16] address @simonjayhawkins's comments

---
 doc/source/whatsnew/v1.1.0.rst | 2 +-
 pandas/core/generic.py         | 6 +++---
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/doc/source/whatsnew/v1.1.0.rst b/doc/source/whatsnew/v1.1.0.rst
index 17bb380a418e4..3ff4e4e7da636 100644
--- a/doc/source/whatsnew/v1.1.0.rst
+++ b/doc/source/whatsnew/v1.1.0.rst
@@ -1068,7 +1068,7 @@ Sparse
 - Bug in :meth:`Series.sum` with ``SparseArray`` raises ``TypeError`` (:issue:`25777`)
 - Bug where :class:`DataFrame` containing :class:`SparseArray` filled with ``NaN`` when indexed by a list-like (:issue:`27781`, :issue:`29563`)
 - The repr of :class:`SparseDtype` now includes the repr of its ``fill_value`` attribute. Previously it used ``fill_value``'s  string representation (:issue:`34352`)
-- Fixed bug where :class:`DataFrame` or :class:`Series` could not be cast to :class:`SparseDtype` when empty (:issue:`33113`)
+- Bug where empty :class:`DataFrame` could not be cast to :class:`SparseDtype` (:issue:`33113`)
 
 ExtensionArray
 ^^^^^^^^^^^^^^
diff --git a/pandas/core/generic.py b/pandas/core/generic.py
index bf48410cd4815..c4559262fbb40 100644
--- a/pandas/core/generic.py
+++ b/pandas/core/generic.py
@@ -5542,15 +5542,15 @@ def astype(
                 self.iloc[:, i].astype(dtype, copy=copy)
                 for i in range(len(self.columns))
             ]
+            # GH 33113: handle empty frame or series
+            if not results:
+                return self.copy()
 
         else:
             # else, only a single dtype is given
             new_data = self._mgr.astype(dtype=dtype, copy=copy, errors=errors,)
             return self._constructor(new_data).__finalize__(self, method="astype")
 
-        if not results:
-            return self.copy()
-
         # GH 19920: retain column metadata after concat
         result = pd.concat(results, axis=1, copy=False)
         result.columns = self.columns

From dcdf11ff2ff2a01b566b61668db453ae9e017ec8 Mon Sep 17 00:00:00 2001
From: Valentin Iovene <valentin@too.gy>
Date: Mon, 22 Jun 2020 17:16:07 +0200
Subject: [PATCH 13/16] revert back to previous solution + add test

---
 pandas/core/generic.py                 | 7 ++++---
 pandas/tests/extension/base/casting.py | 7 +++++++
 2 files changed, 11 insertions(+), 3 deletions(-)

diff --git a/pandas/core/generic.py b/pandas/core/generic.py
index c4559262fbb40..0fd4c6c8c1fee 100644
--- a/pandas/core/generic.py
+++ b/pandas/core/generic.py
@@ -5542,15 +5542,16 @@ def astype(
                 self.iloc[:, i].astype(dtype, copy=copy)
                 for i in range(len(self.columns))
             ]
-            # GH 33113: handle empty frame or series
-            if not results:
-                return self.copy()
 
         else:
             # else, only a single dtype is given
             new_data = self._mgr.astype(dtype=dtype, copy=copy, errors=errors,)
             return self._constructor(new_data).__finalize__(self, method="astype")
 
+        # GH 33113: handle empty frame or series
+        if not results:
+            return self.copy()
+
         # GH 19920: retain column metadata after concat
         result = pd.concat(results, axis=1, copy=False)
         result.columns = self.columns
diff --git a/pandas/tests/extension/base/casting.py b/pandas/tests/extension/base/casting.py
index 3aaf040a4279b..8a6dc5c2c1764 100644
--- a/pandas/tests/extension/base/casting.py
+++ b/pandas/tests/extension/base/casting.py
@@ -56,3 +56,10 @@ def test_astype_empty_dataframe(self, dtype):
         df = pd.DataFrame()
         result = df.astype(dtype)
         self.assert_frame_equal(result, df)
+
+    def test_astype_empty_dataframe_empty_dict(self, dtype):
+        # issue mentioned further down in the following issue's thread
+        # https://github.com/pandas-dev/pandas/issues/33113
+        df = pd.DataFrame()
+        result = df.astype(dict())
+        self.assert_frame_equal(result, df)

From e2d4241016d7270bd360b9dda01064ac70dbf1bc Mon Sep 17 00:00:00 2001
From: Valentin Iovene <valentin@too.gy>
Date: Mon, 22 Jun 2020 17:28:16 +0200
Subject: [PATCH 14/16] move test

---
 pandas/tests/extension/base/casting.py    | 7 -------
 pandas/tests/frame/methods/test_astype.py | 7 +++++++
 2 files changed, 7 insertions(+), 7 deletions(-)

diff --git a/pandas/tests/extension/base/casting.py b/pandas/tests/extension/base/casting.py
index 8a6dc5c2c1764..3aaf040a4279b 100644
--- a/pandas/tests/extension/base/casting.py
+++ b/pandas/tests/extension/base/casting.py
@@ -56,10 +56,3 @@ def test_astype_empty_dataframe(self, dtype):
         df = pd.DataFrame()
         result = df.astype(dtype)
         self.assert_frame_equal(result, df)
-
-    def test_astype_empty_dataframe_empty_dict(self, dtype):
-        # issue mentioned further down in the following issue's thread
-        # https://github.com/pandas-dev/pandas/issues/33113
-        df = pd.DataFrame()
-        result = df.astype(dict())
-        self.assert_frame_equal(result, df)
diff --git a/pandas/tests/frame/methods/test_astype.py b/pandas/tests/frame/methods/test_astype.py
index b06c3d72a2c77..4300d273a74ec 100644
--- a/pandas/tests/frame/methods/test_astype.py
+++ b/pandas/tests/frame/methods/test_astype.py
@@ -557,3 +557,10 @@ def test_astype_dt64tz_to_str(self, timezone_frame):
             assert (
                 "2 2013-01-03 2013-01-03 00:00:00-05:00 2013-01-03 00:00:00+01:00"
             ) in result
+
+    def test_astype_empty_dtype_dict(self, dtype):
+        # issue mentioned further down in the following issue's thread
+        # https://github.com/pandas-dev/pandas/issues/33113
+        df = pd.DataFrame()
+        result = df.astype(dict())
+        self.assert_frame_equal(result, df)

From 7bc6255f750b32a475dad17bd44fa0d5d7bae732 Mon Sep 17 00:00:00 2001
From: Valentin Iovene <valentin@too.gy>
Date: Mon, 22 Jun 2020 17:29:09 +0200
Subject: [PATCH 15/16] fix test

---
 pandas/tests/frame/methods/test_astype.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/pandas/tests/frame/methods/test_astype.py b/pandas/tests/frame/methods/test_astype.py
index 4300d273a74ec..42d114748e769 100644
--- a/pandas/tests/frame/methods/test_astype.py
+++ b/pandas/tests/frame/methods/test_astype.py
@@ -558,7 +558,7 @@ def test_astype_dt64tz_to_str(self, timezone_frame):
                 "2 2013-01-03 2013-01-03 00:00:00-05:00 2013-01-03 00:00:00+01:00"
             ) in result
 
-    def test_astype_empty_dtype_dict(self, dtype):
+    def test_astype_empty_dtype_dict(self):
         # issue mentioned further down in the following issue's thread
         # https://github.com/pandas-dev/pandas/issues/33113
         df = pd.DataFrame()

From 95fd399a40770240c154abf8fa37de6ae0cd2aea Mon Sep 17 00:00:00 2001
From: Valentin Iovene <valentin@too.gy>
Date: Mon, 22 Jun 2020 18:03:09 +0200
Subject: [PATCH 16/16] fix test again

---
 pandas/tests/frame/methods/test_astype.py | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/pandas/tests/frame/methods/test_astype.py b/pandas/tests/frame/methods/test_astype.py
index 42d114748e769..b0fd0496ea81e 100644
--- a/pandas/tests/frame/methods/test_astype.py
+++ b/pandas/tests/frame/methods/test_astype.py
@@ -561,6 +561,7 @@ def test_astype_dt64tz_to_str(self, timezone_frame):
     def test_astype_empty_dtype_dict(self):
         # issue mentioned further down in the following issue's thread
         # https://github.com/pandas-dev/pandas/issues/33113
-        df = pd.DataFrame()
+        df = DataFrame()
         result = df.astype(dict())
-        self.assert_frame_equal(result, df)
+        tm.assert_frame_equal(result, df)
+        assert result is not df